This invention relates generally to improved digital communication means and methods, and more particularly to improved means and methods useful for providing reliable, high speed communication of digital data between units in a digital data processing system.
Modern data processing systems have a number of different units between which binary digital data must be reliably communicated at high speed. For example, in a modern data processing system, it may typically be required to provide for asynchronously controlled digital data communication between a data processing unit and one or more remote units located some 300 feet away.
Although parallel digital data communication has been employed in the prior art for providing digital data communication between data processing units, the current trend is toward the use of serial transmission techniques because of the cost and inconvenience of parallel communication systems, particularly where communication is required to be provided over distances greater than 100 feet. However, in order to make such serial digital data communication compatible with the speed capabilities of modern data processing systems, it is important that the serial digital data transmission system be capable of providing relatively high digital data transmission rates such as, for example, an effective digital data transmission rate of 20 megahertz over a distance of 300 feet.
Although a variety of approaches and circuitry are known in the art for implementing a serial digital data transmission system, the prior art has nevertheless experienced considerable difficulties in providing an economically feasible serial data transmission system capable of reliable performance at the high digital data transmission rates and over the distances required by modern day computer systems.